<p> Nonaqueous poly(methyl methacrylate) latices were prepared by nonaqueous dispersion polymerization of poly(methyl methacrylate) in heptane in the presence of either trimethylsilyl terminated or vinyl terminated polydimethylsiloxane stabilizer. Poly(methyl methacrylate) particles stabilized by vinyl terminated polydimethylsiloxane showed smaller particle sizes than did those stabilized by trimethylsilyl terminated polydimethylsiloxane. Diameters of the various latex preparations ranged from 1.4 to 0.8 μm and silicone content was around 2 mole percent in each case. Differences between the two types of latex were explained in terms of the nucleation mechanism operating during the preparation of the latices and in terms of the type of attachment of the stabilizer chain to the poly(methyl methacrylate) core.</p> <p> The effect of the silicone concentration present during particle formation was investigated. Vinyl terminated polydimethylsiloxane stabilized latex gave better stabilized particles than did methyl terminated polydimethylsiloxane stabilized latex. The results of varying the concentration and type of initiator were consistent with the conclusions about differences in nucleation and grafting mechanisms.</p> <p> The stability of polydimethylsiloxane stabilized poly(methyl methacrylate) particles was investigated in n-heptane. Acidified montmorillonite clay was determined as the optimum catalyst for this latex system. Flocculation set in at 70% of the original silicone content when the siloxane on the particle surface was degraded with montmorillonite clay in a good solvent. Flocculation was irreversible and occurred abruptly. The point of flocculation was reproducible and the rate of flocculation was identical for two different types of silicone stabilized poly(methyl methacrylate) latex.</p> / Thesis / Master of Science (MSc)

In this thesis we used atomic force microscopy (AFM) to investigate systematically the behaviour of both electrostatically stabilised silica and sterically stabilised polystyrene (PS) colloidal systems on freshly cleaved mica substrates. For the silica colloidal nanoparticles we explored the effect of colloidal suspension concentration, particle size, and different application techniques on both the adsorption behaviour and subsequent structuring of the particles. For the PS colloidal nanoparticles we explored concentration effects and experimented with both dip-coating and droplet application techniques. We showed that silica nanoparticles adsorbed onto mica via irreversible adsorption that possessed lateral mobility due to the weak attraction between the nanoparticles and the substrate, facilitating subsequent capillary structuring of the nanoparticles during drying. We associated the effects of volume fraction with Debye screening, and kinetics effects with particle size and volume fraction. We also successfully imaged a partially dried film and showed the role of convective/capillary forces in the structuring of the nanoparticles. Studies with variations in particle size generated a number of different topography structures; with dewetting phenomena observed for 10 nm nanoparticles and the formation of crystalline structures for 100 nm nanoparticles. Spin coating techniques were used to produce even larger crystalline structures of nanoparticles. Size dependent ordering occurred for low concentration samples due to the polydispersity of the colloidal suspension. We showed that acceleration can affect interparticle spacing. We also studied the role of rotational speed on the crystallinity of the particle configurations and showed how fine tuning of rotational speed can generate large scale monolayer crystalline formations of nanoparticles.

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